1. Field of the Invention
The present invention relates to a machining time predicting apparatus of a numerically controlled machine tool, the apparatus calculating a time taken for a tool to move on a designated path according to a NC (numerical control) command.
2. Description of the Related Art
To predict beforehand a processing time by a numerically controlled machine tool is important for efficiently operate the machine tool. In order to predict the processing time, a user has to know a moving speed of a tool. A method described below has been known as a method of predicting an actual moving speed of a tool.
Japanese Patent Application Laid-Open (JP-A) No. 2007-25945 describes a technique described below. Specifically, in this technique, a database of a speed control parameter, which is set according to at least either one of a type of a processing machine and a machining mode, is made. NC data (NC command) having a program of moving command data is input to a processing time predicting module. The speed control parameter according to the selected type of the processing machine or the machining mode is read from the processing time predicting module, and the processing time is predicted based upon the read speed control parameter and the moving command.
JP-A No. 2009-98981 describes a technique described below. Specifically, in this technique, a divided trajectory that is obtained by dividing a trajectory of a tool into a small section. The tool is moved on the divided trajectory with a speed according to the designated moving speed so as to process a workpiece. A tool position at an optional position on the divided trajectory when the tool is moved as described above and a temporal change of the moving speed of the tool in each axial direction on each of the divided trajectories are obtained as axis control data. A processing time is calculated from the temporal change of the moving speed in each axial direction designated by the obtained axis control data.
JP-A No. 2005-301440 describes a technique described below. Specifically, in this technique, a movement trajectory designated to a machine tool in an axis moving command is interpolated with the same interpolation algorithm as that for driving an NC machine tool (numerically controlled machine tool). The number of times of the interpolation of the movement trajectory designated by the axis moving command is counted, wherein an axis moving time in the axis moving command is calculated by multiplying an interpolation period upon driving and controlling the NC machine tool by the counted number of times of the interpolation.
As described above, a user has to know a moving speed of a tool in order to predict a processing time. However, the actual speed of the tool during machining is different from the speed obtained by applying the acceleration and deceleration, which are set to the CNC parameter, to the designated speed given by an NC command.
The current CNC controls the moving speed of the tool with a very short period in order to suppress shock to a machine and to realize a smooth movement of the tool. Therefore, the moving speed of the tool in a tangential direction along a tool path momentarily changes. Accordingly, in the method of changing the speed in a block unit as described in JP-A No. 2007-25945, an effect of the speed that changes in a unit time shorter than the block length cannot be taken.
In a process that takes time such as die machining, it is important that a time (processing time) taken for the prediction is short, in addition to the precision of the predicted machining time. The technique described in JP-A No. 2009-98981 takes time for a calculation, because the movement of the tool is divided into an operation for each axis in order to use speed data for every axis. Therefore, this technique takes much processing time. The technique described in JP-A No. 2005-301440 utilizes the interpolation process of the CNC. Therefore, most of the functions of the CNC, i.e., from the reading of the NC command to the interpolation, are to be executed, whereby it is impossible to drastically shorten the processing time compared to an actual machining.